Grease 4 x 125ml (4fl oz) ramekins with a little melted butter and dust with cocoa powder, shaking out any excess. Preheat the oven to 190°C/fan 170°C/gas 5. Using an electric whisk, cream the 175g (6oz) butter and caster sugar together until you get a light, creamy texture. Next, add the eggs one at a time, beating well between each addition. Mix the 50g (1¾oz) cocoa powder and golden syrup together in a separate bowl to form a paste then add this to the butter and eggs. Beat it in and then fold in the flour, salt and pistachios. Divide the mixture between the ramekins and bake for 14 minutes. While these are baking make the chocolate sauce by melting the chocolate, cream and rum together in a bowl over a pan of simmering water, making sure the bowl doesn't touch the water. Once melted, gently mix the sauce together. Turn the puddings out into serving bowls, spoon the sauce over and scatter on a few more pistachios. Serve with a generous helping of crème fraîche.